In order to improve heavy load discharge characteristics, there has been proposed that zinc powder as a negative active material is pulverized to reduce internal resistance (for example, U.S. Pat. No. 6,284,410). However, this increases reaction efficiency of a negative electrode, and causes a battery to generate intense heat in case of short circuit, and thus the degree of pulverization of zinc powder is limited in practice.
As a method for preventing rapid temperature increase of a battery in case of short circuit, providing a PTC element having a function of blocking a short circuit current in the battery has been considered.
For example, Japanese Patent Laid-Open No. 2003-217596 proposes that a surface of a negative current collector is coated with an electronic conductor mainly composed of polyethylene and having a PTC function. Japanese Patent Laid-Open No. 9-199106 proposes a lithium secondary battery in which a flange of a sealing plate peripheral edge is crimped via a gasket at an opening end of an external can, including a PTC element placed between the flange of the sealing plate and the gasket.
However, in Japanese Patent Laid-Open No. 2003-217596, the electronic conductor coated on the surface of the negative current collector increases contact resistance with an active material to prevent a current collecting effect, which may reduce discharge performance. The electronic conductor is easily decomposed by an alkaline electrolyte, and the PTC function is sometimes insufficiently exerted.
The lithium secondary battery in Japanese Patent Laid-Open No. 9-199106 has a structure of a sealing portion such as a current collector or an explosion-proof mechanism different from a structure in an alkaline battery, and thus an assembling manner of the PTC element suitable for the structure of the alkaline battery needs to be considered.
Thus, in order to solve the conventional problems, the present invention has an object to provide an alkaline battery that has low internal resistance and superior heavy load discharge characteristics, and is high in safety and reliability.